Question

using a quadratic formula to find the zeros of the function round to Tenth if necessary y equals x squared - 21

Answer 1

y = x^2 - 21
The roots occur when y = 0
x^2 - 21 = 0 Add 21 to both sides.
x^2 = 21 Take the square root of both sides.
sqrt(x^2) = sqrt(21)
x = +/- 4.583

I've enclosed a graph to make sure that you can see what the answer means.